FOAMED ELECTRICAL WIRE AND PRODUCTION METHOD FOR SAME

{Problems} To provide a foamed electrical wire having a fine dielectric breakdown voltage and a method of producing the foamed electrical wire. {Means to solve} The foamed insulating layer 2 contains a thermoplastic resin having heat resistant and has an average bubble diameter of 5 µm or less. It is preferable that the effective dielectric constant of the foamed insulating layer 2 is 2.5 or less, and the foamed insulating layer 2 contains preferably any of polyphenylene sulfide, polyethylene naphthalate, polyethylene telephthalate, polyether ether ketone and a thermoplastic polyimide, more preferably includes a crystalline thermoplastic resin. Furthermore, it is preferable to contain a non-foamed outer skin layer outside of the foamed insulating layer 2, or contain a non-foamed inner skin layer inside of the foamed insulating layer 2, or contain the both skin layers.